Sunday, 10 June 2012

Mobile broadbandLast updated: August 25, 2010. You love the speed and convenience of broadband—but there's a snag: it's tied to your home telephone line. If you're a "road warrier", often working away from home, or you have a long commute into work each day, maybe using your laptop on the train or the bus, a fixed broadband connection isn't much help. What you need is a broadband connection you can take with you—the broadband equivalent of your cellular (mobile) phone. Until recently, using a laptop with a mobile phone was a nightmarishly painful experience. The fastest speed you could achieve working in this way was a measly 9.6 kbps (roughly five times slower than a typical dial-up Internet connection). It really was excruciatingly slow! Now, thanks to hugely improved cellphone networks, you can get broadband-speed, wireless Internet access through a mobile phone connection wherever you happen to be. How does mobile broadband work? Let's take a closer look! Photo Left: This is all you need to go online with mobile broadband. Technically, it's an HSDPA broadband wireless modem made by ZTE—but the phone companies call them "dongles". The dongle simply plugs into your laptop's USB socket. Right: An alternative mobile broadband dongle made by Huawei Technologies. This one attaches with the short silver USB cable you can see coming out at the bottom right. My dongle even came with a little bit of Velcro so I could attach it conveniently to my laptop. Both these dongles were supplied by the UK wireless company 3; in the United States, mobile broadband is offered by such companies as Sprint, Verizon, and AT&T.

How does mobile broadband work?

Mobile broadband is a really simple idea, but the specifics are quite complex. In this article, we'll give you a quick overview for starters, followed by a much more detailed explanation for those who want it. If you're not familiar with how ordinary cellphones work, how the Internet works, or what makes broadband different from dial-up, you may want to start with some of those articles first and come back here afterwards.

Broadband on a cellphone network

Cellular phones were largely inspired by landlines (traditional telephones wired to the wall) and worked in a very similar way—until recently. A landline effectively establishes a permanent connection—an unbroken electrical circuit—between your phone and the phone you're calling by switching through various telephone exchanges on the way: this is called circuit switching. Once a landline call is in progress, your line is blocked and you can't use it for anything else. If you have broadband enabled on your telephone line, the whole thing works a different way. Your telephone line is split into two bits: a voice channel, that works as before, by circuit switching, and a data channel that can constantly send and receive packets of digital data to or from your computer by packet switching, which is the very fast and efficient way in which data is sent across the Internet. (See our article on the Internet if you want to know more about the difference between circuit switching and packet switching.)As long as cellphones were using circuit-switching technologies, they could work only at relatively slow speeds. But over the last decade or so, most service providers have rolled out networks that use packet-switching technologies. These are referred to as third-generation (3G) networks and they offer data speeds similar to low-speed landline broadband (typically 350kbps-2MBps). Over time, engineers have found ways of making packet-switching cellphone networks increasingly efficient. The current hot technology is known as HSDPA (High-Speed Downlink Packet Access), HSPA, or "3.5G" and it's up to five times faster than 3G.

How do you use HSDPA?

You can use HSDPA in two ways. If you have a reasonably new cellphone, HSPDA will let you download music and videos to your phone at high (broadband) speeds. Unlike with a traditional phone call, where you pay for access by the minute, with HSDPA you pay by the amount you download. So your mobile phone provider might sell you a certain number of megabytes or gigabytes for a fixed fee.The other way to use HSDPA (and the way I use it) is as a way of getting online with a laptop when you're on the move. You buy a "dongle" (which is a very small, lightweight HSDPA modem that plugs into the USB socket of your laptop), buy some access time from a service provider, plug your dongle into the laptop, and away you go. The dongle has built-in software so it automatically installs itself on your PC. I was up and running with my mobile broadband in less than five minutes. Think of your dongle as a cross between a modem and a cellphone—but, because it has no battery or screen, it's a fraction of the weight of a cellphone and somewhat smaller.Photo: Another view of my broadband dongle, this time photographed from underneath. You can see the SIM card drawer opened up with the SIM card exposed. You need a SIM card in your dongle to give you access to your phone network. It's identical to the SIM card you'd use in a cellphone (indeed, you can take it out and use it in a cellphone to make calls if you want to).

How good is mobile broadband?

If you need to use broadband on the move, it's a brilliant solution. Anywhere you can get a good (HSDPA) signal, you can get high-speed broadband. Where there is no HSDPA network coverage, your broadband will work at 3G speeds (less than about 300kbps)—but that's still about seven times faster than a dial-up landline connection. Depending on which country you're in and where you live and work, you may find HSDPA mobile broadband has much better overall coverage than Wi-Fi—in other words, you can go online in far more places—and it can work out far cheaper too. The drawback is that you're using a cellphone network for your access, so the quality of your connection can vary drastically. If you're working on a train, for example, you can expect to be regularly connected and disconnected as you move in and out of cell coverage—just as a cellphone call gets cut off when you go through tunnels and under bridges. Right now, I seem to be working on the edge of a cell, so the quality of my connection is constantly flickering between HSDPA and 3G and my connection speed is varying from moment to moment. So the erratic quality of my broadband service, at this moment, does not compare very well with what I'd get from a Wi-Fi hotspot. But the nearest hot-spot is five miles away and would charge me as much for a couple of hours access as I pay for a whole month of mobile broadband, so I have no real reason to complain.Two bits of advice, then: if you plan on using your mobile broadband in certain specific locations most of the time, you need to check out the network coverage in those places before you buy. Most phone service providers publish maps of their coverage, but there is no substitute for checking the coverage by using the system for real. (In the UK, the 3 cellphone company I use allows customers a couple of days grace after taking delivery of the USM broadband modem to try out the network coverage. If you're not happy you can return the equipment for a refund.)All told, I've found mobile broadband the best solution to working on the move. It's infinitely faster than a dial-up mobile, it's much faster than a dial-up landline, and it's cheaper and more convenient than Wi-Fi. I love it!

How will mobile broadband develop in future?

Cellphone companies are very excited about mobile broadband. According to a forecast by OVUM Strategy Analytics and cellphone makers Ericsson, mobile wireless broadband users are growing much faster than fixed (landline) broadband users. By 2012, there will be over 1.8 billion broadband Internet users worldwide and more people will be using mobile broadband than landline broadband. HSDPA is expected to capture up to three quarters of the mobile market, though it will face a bit of competition from other systems, including one called mobile WiMAX.

The more detailed explanation

Now for a slightly more technical explanation of HSDPA—but first it helps if we understand a little bit about the mobile phone systems that preceded it and how they've evolved from one another.

Analog landlines

Imagine you want to make lots of money by setting up a telephone company in your area. Back in the 1950s, you would have had to run separate telephone lines to the homes of all your customers. In effect, you would have given each customer a separate electrical circuit that they could use to connect to any other customer via some central switching equipment, known as the exchange. Phone calls made this way were entirely analog: the sound of people's voices was converted into fluctuating electrical signals that travelled up and down their phone lines.

Analog cellphones

By the 1970s, mobile telephone technology was moving on apace. You could now give your customers cellphones they could use while they were on the move. Instead of giving each person a wired phone, what you gave them was effectively a radio handset that could transmit or receive by sending calls as radio waves of a certain frequency. Now if everyone uses the same frequency band, you can theoretically hear other people's calls. So, in practice, you divide the frequency band available into little segments and let each person send and receive on a slightly different frequency. This system is called frequency-division multiple access (FDMA) and it's how the early analog phones worked (cordless landline telephones still work this way). FDMA simply means lots of people use the mobile phone system at once by sending their calls with radio waves of slightly different frequency. FDMA was like a radio version of the ordinary landline phone system and, crucially, it was still analog. FDMA cellphones were sometimes called first-generation (1G) mobile phones.

Digital cellphones

The trouble with FDMA is that frequencies are limited. As millions of people sought the convenience of mobile phones ("phones to go"), the frequency band was soon used up—and the engineers had to find a new system. First, they swapped from analog to digital technology: phone calls were transmitted by sampling the sound of people's voices and turning each little segment into a numeric code. As well as sharing phone calls between different frequency bands, the engineers came up with the idea of giving each phone user a short "time share" of the band. Effectively, the mobile phone system splits up everyone's calls into little digital chunks and sends each chunk at a slightly different time down the same frequency channel. It's a bit like lots of people being in a crowded room together and taking it in turns to talk so they don't drown one another out. This system is called time-division multiple access (TDMA) and it's a big advance on FDMA. GSM cellphones, based on TDMA, were the second generation (2G) of mobile phones.Photo: Before HSDPA: Web browsing on a cellphone with an earlier system called WAP, which never really caught on. See our article on wireless Internet for more details.

High-speed digital cellphones

Even TDMA isn't perfect. With the number of phone users increasing so fast, the frequency bands were still getting overcrowded. So the engineers put their thinking caps on again and found yet another way to squeeze more users into the system. The idea they came up with next was called code-division multiple access (CDMA) and uses elements of both TDMA and FDMA so a number of different callers can use the same radio frequencies at the same time. CDMA works by splitting calls up into pieces, giving each piece a code that identifies where it's going from and to. It's effectively a packet-switching technology similar to the way information travels across the Internet and it can increase the overall capacity of the phone system by 10-20 percent over TDMA. Basic CDMA evolved into an even higher-capacity system called Wideband CDMA (WCDMA), which sends data packets over a wide band of radio frequencies so they travel with less interference, and more quickly and efficiently (an approach known as spread-spectrum). WCDMA is an example of a third generation (3G) cellphone system. The 3G equivalent of GSM is known as UMTS.

"Broadband" cellphones

Ordinary CDMA is great for sending phone calls, which involve two-way communication. But it's not so good for providing Internet access. Although Net access is also two-way (because your computer is constantly requesting Web pages from servers and getting things back in return), it's not a symmetrical form of communication: you typically download many times more information than you upload. Fast home broadband connections achieve their high speeds by splitting your phone line into separate voice and data channels and allocating more data channels to downloading than to uploading. That's why broadband is technically called ADSL—the A stands for asymmetric (and DSL means digital subscriber line).Think of HSDPA as a kind of broadband, cellular ADSL. It's a variation of CDMA that is designed for downloading: for sending lots of data to broadband cellphones or laptops attached with mobile broadband modems. It's optimized in various different ways. First, like ADSL, it introduces a high-speed downloading channel called HS-DSCH (High Speed Downlink Shared Channel), which allows lots of users to download data efficiently at once. Three other important features of HSDPA are AMC (adaptive modulation and coding), fast base-station scheduling (BTS), and fast retransmissions with incremental redundancy. What does all that stuff mean?

AMC (Adaptive modulation and coding) simply means that the cellphone system figures out how good your connection is and changes the way it sends you data if you have a good connection. So if you're in the middle of a cell (near a cellphone antenna base station), you'll get more data more quickly than if you're at the edge of a cell where reception is poor. flash memory, and use the generic software supplied by the manufacturer on your PC instead of your provider's customized software. Before you go any further, be sure to write down all the connection settings for your current provider (look in the control panel of your dongle's PC software). You will need them later. Next, go to the dongle manufacturer's website (it's probably a company such as Huawei), download the latest firmware package, and follow the instructions to load it into your dongle. Make sure you get exactly the right firmware to match your dongle's model number. Follow the manufacturer's instructions to the letter!

Fast base-station scheduling means that the base station figures out when and how users should be sent data, so the ones with better connections get packets more often.

In any packet-switching system, packets sometimes get lost in transmission, just as letters get lost in the regular mail. When this happens, the packets have to be retransmitted—and that can take time. With ordinary CDMA technologies, retransmissions have to be authorized by a top-level controller called the radio network control (RNC). But with HSDPA, retransmissions are organized by a system closer to the end user, so they happen more quickly and the overall system is speeded up. Incremental redundancy means the system doesn't waste time retransmitting bits of data that successfully got through first time.

Put all this together and you have a cellphone system that's optimized for sending out packets of data to many users at once. Because it's better than 3G, they call it 3.5G. But it won't be long before we have 4G, 5G, 6G and all the rest. Those systems are already on the way. Look out soon for improved systems called HSDPA Evolved, offering download speeds of 24-42 Mbps, and 3G LTE (Long Term Evolution), promising 50Mbps-100Mbps.

How to upgrade your dongle or switch mobile broadband providers

Warning!

The advice provided here is for general guidance only. Do not follow it unless you are technically qualified. We take no responsibility for any loss or damage that may result.

There is a chance you could damage your dongle or stop it from working properly.

If you change the firmware in your dongle, you may breach your contract with your service provider. You'll almost certainly find they do not give you any technical support if you get into trouble.

You may not be able to undo the changes you've made and restore your dongle to how it was before.

If you've bought a mobile dongle from a cellphone service provider, it will almost certainly have been customized by that company with their own software. For example, if you buy a dongle from the phone company 3, you'll get some PC software branded with the 3 logo that automatically connects to 3's service when you plug in your dongle. But you can still use your dongle with other providers, such as Vodafone! You can also upgrade your dongle to use newer software from the manufacturers, often getting a more reliable signal and higher speeds.The way to do this is to change the firmware (preloaded software) in the dongle, which is stored in The next time you use your dongle, you'll find it runs a more generic version of the connection software branded with the manufacturer's logo (i.e. Huawei, or whoever it might be) rather than the service provider's, and you'll have to enter your connection settings manually the first time. You should find the dongle works perfectly, as before—it may even work faster and more reliably now because you're using newer software. To use a different provider, all you need to do is swap over your SIM card and enter the connection settings for your new provider using the PC software.

Photo (left): This is the 3-branded software that used to pop up on my screen when I used 3 mobile's HSDPA service. You can see that I'm getting a maximum speed of 479 kbps, which is a fairly modest broadband speed, but about 10 times faster than I'd get with dial-up.Photo (right): This is the manufacturer's own version of essentially the same software, called Huawei Mobile Connect. This is what you'll see if you flash the firmware of your dongle. It works the same but just looks a little bit different. Connection speeds are shown on the right (the modem wasn't actually connected when this screenshot was taken).